The present invention relates generally to a method of controlling the control effectors of an aerodynamic vehicle and, more particularly, to an integrated method for controlling the control effectors of an aerodynamic vehicle, including the aerodynamic surfaces, thrust variations and nozzle vectoring, in order to efficiently cause a desired change in the time rate of change of the system state vector of the aerodynamic vehicle during various stages of flight.
During flight, the control of aerodynamic vehicles, such as aircraft, is principally accomplished via a variety of flight control effectors. These flight control effectors include aerodynamic controls such as the rudder, elevators, ailerons, speed brakes, engine thrust variations, nozzle vectoring and the like. By altering the various flight control effectors, the system state vector that defines the current state of the aerodynamic vehicle can be changed. In this regard, the system state vector of an aerodynamic vehicle in flight typically defines a plurality of current vehicle states such as the angle of attack, the angle of side slip, the air speed, the vehicle attitude and the like.
Historically, the flight control effectors were directly linked to various input devices operated by the pilot. For example, flight control effectors have been linked via cabling to the throttle levers and the control column or stick. More recently, the flight control effectors have been driven by a flight control computer which, in turn, receives inputs from the various input devices operated by the pilot. By appropriately adjusting the input devices, a pilot may therefore controllably alter the time rate of change of the current system state vector of the aerodynamic vehicle.
Unfortunately, flight control effectors may occasionally fail, thereby adversely affecting the ability of conventional control systems to maintain the dynamic stability and performance of the aerodynamic vehicle. In order to accommodate failures of one or more of the flight control effectors, control effectors failure detection and flight control reconfiguration systems have been developed. These systems typically remove the flight control effectors that has been identified as inoperable from the control system. These systems are therefore designed to detect the failure of one or more flight control effectors and to alter the control logic associated with one or more of the flight control effectors that remain operable in an attempt to produce the desired change in the time rate of change of the current system state vector of an aerodynamic vehicle requested by the pilot. These failure detection and flight control reconfiguration systems are highly complex. As such, the proper operation of these systems is difficult to verify. Moreover, these systems introduce a risk that a flight control effector that is actually functioning properly may be falsely identified as having failed and thereafter removed from the control system, thereby potentially and unnecessarily rendering the control system less effective.
Additionally, the control effectors of an aerodynamic vehicle generally have some limitations on their performance. In this regard, the rate of change accommodated by most control effectors is generally limited to a range bounded by upper and lower limits. By way of example, for aircraft, such as direct lift aircraft, that permit nozzle vectoring, the actual position which the nozzles may assume is typically limited to within upper and lower limits. Unfortunately, conventional control systems do not accommodate limitations in the range of settings and rate of change of the control effectors. As such, conventional control systems may attempt to alter a control effector in a manner that exceeds its limitations. Since the control effector will be unable to make the desired change, the control system may correspondingly fail to produce the desired change in the time rate of change of the system state vector of the aircraft.
In addition to the aerodynamic surfaces commonly utilized to control the flight of an aerodynamic vehicle, aircraft has been developed that can provide additional control by means of thrust variations and/or thrust or nozzle vectoring. For example, some multi-engine aircraft permit the plurality of engines to be driven differently so as to generate different levels of thrust which, in turn, can serve to assist in the controlled flight of the aircraft. As another example, vectoring nozzles that may be commanded to assume any of a range of positions and bi-directional nozzles that direct the exhaust in one of two directions have been developed. By controllably directing at least a portion of the engine exhaust in different directions, vectoring nozzles, which shall hereafter also generally include bi-directional nozzles, can also assist in the controlled flight of the aircraft.
While various control systems have been developed to control the flight control effectors during flight, these control systems generally do not integrate the control provided by aerodynamic surfaces during flight with the control needed in instances in which the aircraft has no, or a negligible, velocity such that the aerodynamic control surfaces, such as the rudder, elevators, ailerons or the like, do not significantly contribute, if at all, to the lift and attitude control of the aircraft. In this regard, direct lift aircraft have been and are being developed. Direct lift aircraft have control effectors, such as vectoring nozzles or bi-directional nozzles, that can direct the engine exhaust in different directions to provide lift and attitude control of the aircraft. By appropriately positioning the nozzles, a direct lift aircraft can takeoff and land in a substantially vertical manner. As such, during takeoff and landing, the aerodynamic control surfaces do not significantly contribute to the lift and the attitude control of the direct lift aircraft. Instead, the lift and attitude control are principally provided and controlled by any thrust variations provided by the engines and the vectoring of the associated nozzles.
In order to control the lift and attitude of an aircraft during a vertical takeoff or landing, control systems have been developed to control the engines and the associated nozzles. For example, one control system employs an optimization algorithm, termed an L1 optimization algorithm. While generally effective, this optimization algorithm suffers from several deficiencies. In this regard, the optimization algorithm is computationally complex, thereby requiring substantial computing resources and being difficult and costly to expand or scale to accommodate more sophisticated control schemes, such as the control scheme necessary to control vectoring nozzles as opposed to simpler bi-directional nozzles. The computational complexity of the optimization algorithm may also cause the solution to be approximated in instances in which the optimization algorithm cannot arrive at an exact solution within the time frame required to maintain stability of the aircraft. In addition, the optimization algorithm may not converge in all situations. In instances in which the optimization algorithm may not converge, the prior solution, i.e., the solution from a prior iteration of the optimization algorithm, would continue to be utilized, thereby resulting in a sub-optimal solution.
As such, it would be desirable to provide an improved control system that effectively integrates the various control effectors including the aerodynamic surfaces and the thrust variations and nozzle vectoring so as comprehensively control the aerodynamic vehicle during different stages of flight, including for example, the vertical takeoff and landing of a direct lift aircraft during which thrust variations and nozzle vectoring dominate the control scheme as well as in flight during which the aerodynamic surfaces provide a greater measure of control. In addition, it would be desirable to develop a method of controlling the control effectors of an aerodynamic vehicle, such as a direct lift aircraft, which provides increased flexibility with respect to the removal or inclusion of a flight control effector that may have failed. In addition, it would be advantageous to provide a method for controlling the control effectors of an aerodynamic vehicle, including a direct lift aircraft, in a manner that recognizes and accommodates limitations in the settings and rate of change of at least some of the control effectors.
An improved method and computer program product are therefore provided for controlling the plurality of control effectors of an aerodynamic vehicle in order to efficiently bring about a desired change in the time rate of change of the system state vector of the aerodynamic vehicle. Advantageously, the method and computer program product provide an integrated control scheme for controlling thrust variations and nozzle vectoring, as well as various aerodynamic surfaces throughout all phases of flight including takeoff, flight and landing. By integrating the control of thrust variations and nozzle vectoring with the control of aerodynamic surfaces, the method and computer program product can also provide control during vertical takeoff and landing scenarios.
The method and computer program product of one aspect of the present invention permits the control of the control effectors to be tailored based upon predetermined criteria, such as the relative importance of the respective states of the aerodynamic vehicle and/or the weighting to be given to any outlier measurements. According to another aspect, the method and computer program product control the plurality of control effectors while recognizing limitations upon the permissible changes to at least one control effector, such as limitations upon the rate of change or the range of positions of at least one control effector. As such, the method and computer program product of the present invention address the shortcomings of conventional control systems and efficiently command the control effectors so as to alter the time rate of change of the system state vector of the aerodynamic vehicle in a desired manner.
The method and computer program product control the control effectors of an aerodynamic vehicle by initially determining the current commanded state of the plurality of control effectors including, for example, the current commanded position of each nozzle, the current commanded level of thrust for each engine and the current commanded position of at least one aerodynamic surface. The method and computer program product then determine the differences between anticipated changes in the plurality of states of the aerodynamic vehicle based upon the current state of each control effector and the current flight conditions, and desired changes in the plurality of states of the aerodynamic vehicle. In order to determine the differences between the anticipated and desired changes in the plurality of state rates of the aerodynamic vehicle, the dot product of a vector representing the current commanded state of each control effector and a matrix representing changes in the plurality of states of the aerodynamic vehicle in response to changes in the control effectors at the current flight conditions is initially determined. In this regard, the matrix includes a plurality of terms, each of which represents the anticipated change in a respective state rate of the aerodynamic vehicle in response to the change of a respective control effector at the current flight conditions. By considering the effect of changes in a control effector at the current flight conditions, the method and computer program product can rely upon the control provided by thrust variations and nozzle vectoring more heavily during vertical takeoff and landing and upon the control provided by aerodynamic surfaces more heavily once in flight, thereby providing an integrated and robust control scheme. In order to determine the difference between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle, the vector difference between the dot product and a vector representing the desired change in the plurality of states of the aerodynamic vehicle is obtained in one embodiment.
According to one aspect of the present invention, the differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle are then weighted based upon a predetermined criteria. In this regard, the differences may be weighted based upon the relative importance of the respective states of the aerodynamic vehicle, thereby permitting those states which are believed to be of greater importance to be assigned a correspondingly greater weight. As a result of this greater weight, the method and computer program product of this aspect of the present invention will control the control effectors so as to more quickly alter these states than other states having lower weights assigned thereto. In addition or in the alternate, the differences may be nonlinearly weighted by a predefined penalty based upon the emphasis to be placed upon outliers, i.e., relatively large differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle. A predefined penalty may also be utilized to emphasize the importance of certain relationships, such as maintaining area match for each engine, with relatively large penalties being assigned to variations from the desired relationship.
Based upon the weighted differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle, the method and computer program product may determine a second dot product of the weighted vector difference and a transpose of the matrix representing changes in the state rates of the aerodynamic vehicle in response to changes in the plurality of control effectors. The second dot product therefore represents the changes in the control effectors required to affect the desired changes in the plurality of states of the aerodynamic vehicle, given the anticipated changes in the plurality of states. As such, the weightings assigned to the respective states of the aerodynamic vehicle will correspondingly effect changes in the desired state of the control effectors. By utilizing the transpose of the matrix representing changes in the state rates of the aerodynamic vehicle in response to changes in the control effectors, the method and computer program product effectively cause the control effectors that will have the greatest impact upon effecting the desired change to be adjusted to a greater degree than the control effectors that will have less impact upon effecting the desired change, thereby improving the efficiency of the control scheme. The second dot product may also be weighted by a gain matrix, one term of which is associated with each control effector in order to appropriately weight the relative contributions of the control effectors.
According to another advantageous aspect of the present invention, the method and computer program product may also limit the permissible changes of at least one of the control effectors. In this regard, the permissible rate of change of one or more of the control effectors may be limited. Similarly, the position of one or more of the control effectors may also be limited to within a predefined range. As such, the method and computer program product of the present invention effectively recognize and accommodate limitations of the control effectors, thereby preventing any attempts to drive the control effectors beyond their predefined limitations.
The method and computer program product then issue control signals to the plurality of control effectors so as to implement at least a portion of the desired change in the time rate of change of the system state vector of the aerodynamic vehicle. In those aspects of the present invention in which the differences between the anticipated and desired changes in the plurality of states of the aerodynamic vehicle are weighted, the control signals are at least partially based upon the weighted differences. More particularly, in those embodiments in which the second dot product of the weighted vector difference and the transpose of the matrix representing changes in the system state vector of the aerodynamic vehicle in response to the changes in the plurality of control effectors is determined, the control signals are at least partially based upon the second dot product. Moreover, the control signals may be more directly weighted by the gain matrix. Additionally, in those aspects of the present invention in which the permissible changes of at least one of the control effectors is limited, the control signals issued to the control effectors are subject to the limitations in the permissible changes of one or more of the control effectors. Thus, at least a portion of the desired change in the plurality of states of the aerodynamic vehicle may be implemented without exceeding the permissible changes of the control effectors.
Thus, the method and computer program product of the present invention provide an improved technique for efficiently controlling the control effectors of an aerodynamic vehicle in order to effect the desired change in the time rate of change of the system state vector of the aerodynamic vehicle. Advantageously, the method and computer program product provide an integrated control scheme for controlling thrust variations and nozzle vectoring, as well as various aerodynamic surfaces throughout all phases of flight including takeoff, flight and landing. According to one aspect of the present invention, the control of the control effectors may be influenced by weighting based upon a predetermined criteria, thereby permitting the control system to be more individually tailored and efficiently implemented. According to another aspect of the present invention, the permissible changes of one or more of the control effectors may be limited such that the desired change in the time rate of change of the system state vector of the aerodynamic vehicle may be affected without attempting to exceed the permissible changes of at one or more of the control effectors.